1. Field of the Invention
This invention relates to a pellet bonding apparatus used in semiconductor manufacture processes.
2. Description of the Background Art
As a process concerning semiconductor manufacture, there is a pellet bonding process using a pellet bonding apparatus. In this process, each pellet is taken out from a wafer ring unit installed on a wafer stage by a suction nozzle of a pellet removal/transfer unit, then put on a rotary table of a pellet position correcting mechanism, then corrected to make up for deviation of position, if necessary, by causing rotation of the rotary table, and then picked up from the rotary table and bonded to a lead frame by a suction nozzle of a bonding mechanism.
In this prior art pellet bonding apparatus, the suction nozzle of the pellet removal transfer mechanism removes a pellet 2 either in a right half area A of wafer 1, as shown in FIG. 9A, or in a left half area B of the wafer 1, as shown in FIG. 9B. In the former case of FIG. 9A, when the removed pellet 2 is put on the rotary table 3 of the pellet position correcting mechanism, its position is detected directly, i.e., without rotation of the rotary table 3, using a camera. Subsequently, its position is corrected, if necessary, by causing rotation of the rotary table 3. Then, it is removed from the rotary table 3 and bonded to a lead frame 4 by the suction nozzle of the bonding mechanism.
In the latter case of FIG. 9B, however, the wafer stage with the wafer ring unit installed thereon is rotated by 180 degrees for removing the pellet 2 from the area B of the wafer 1 with the suction nozzle of the pellet removal/transfer mechanism. Then, when the removed pellet 2 is put on the rotary table 3, the rotary table is rotated by 180 degrees and the position of the pellet 2 is detected using the camera. Then, the pellet 2 is corrected, if necessary, by causing rotation of the rotary table 3, and then bonded to the lead frame 4 using the suction nozzle of the bonding mechanism.
As is seen, in the latter case, in which the pellet 2 is removed from the area B of the wafer 1, it is necessary to rotate the rotary stage 3 by 180 degrees, thus producing a delay time till the end of rotation of the rotary table 3, as shown by phantom line in FIG. 3. That is, the delay time causes delay of the subsequent step of correcting the position (i.e., orientation) of the pellet 2 and step of bonding the pellet 2 by bonding head. As a consequence, increased time is required for the overall operation of bonding the pellets 2 in the areas A and B.
One pellet bonding apparatus of the above type has a wafer sheet expander for expanding a wafer sheet with a wafer applied thereto, as disclosed in, for instance, Japanese Patent Laid-Open No. Hei 4-68553.
The disclosed wafer sheet expander 101 is shown in FIG. 10. As shown, it includes an expander ring 102 and a Press ring 103 disposed on the outside of the expander ring 102 and capable of displacement in the axial direction of the expander ring 102. A wafer sheet 105 with a wafer 104 applied thereto, is put on the end of the expander ring 102, and it is expanded on the end of the expander ring 102 by pushing down the wafer ring 106, to which the wafer sheet 105 is secured, with the press ring 103.
With the expanding of the wafer sheet 105 caused in this way, gaps are formed between adjacent ones of a large number of pellets 107 into which the wafer 104 is diced, thus facilitating the take-up of each the pellets 107.
In this prior art example, however, with the lowering of the press ring 103 the wafer sheet 105 is expanded in direct contact with the end of the expander ring 102. Therefore, the frictional resistance between the wafer sheet 105 and the end of the expander ring 102 is so high as to possibly result in failure of uniformly expanding the wafer sheet 105.
SUMMARY OF THE INVENTION
A first object of the invention in view of the above circumstances is to provide a pellet bonding apparatus which permits the pellet bonding operation to be carried out in a short period of time.
A second object of the invention is to provide a pellet bonding apparatus, which has a wafer sheet expander for expanding a wafer sheet uniformly to form optimum gaps between adjacent pellets.
To attain the above first object of the invention, there is provided a pellet bonding apparatus, which comprises a wafer stage capable of installation thereon of a wafer ring unit having a group of pellets each separated from a wafer, a pellet removal/transfer mechanism for removing pellets one by one from the pellet group of the wafer ring unit at a pellet removal position and transferring each removed pellet, a pellet position correcting mechanism for setting each removed pellet on a rotary table and correcting the position of the pellet, and a bonding mechanism for removing each pellet having been position corrected by the pellet position correcting mechanism and bonding the removed pellet to a lead frame, the wafer stage permitting rotation of the wafer ring unit by each angle corresponding to each of a plurality of areas, which the pellet group of the wafer ring unit is divided into, the pellet position correcting mechanism being capable of correcting pellet position by causing rotation of the rotary table by a predetermined angle in either a forward or reverse direction independently of the rotation of the wafer ring unit such that each pellet has the same orientation when removed by the bonding mechanism.
Thus, according to the invention it is possible, regardless of whether the wafer stage has been rotated by a predetermined angle, to obtain the setting of the same pellet orientation at all times of removing a pellet with rotation of the rotary table of the pellet position correcting mechanism through a predetermined angle. It is thus possible to set the angle of rotation of the rotary table so that the required orientation correction is small. This means that it is possible to curtail time until the completion of the subsequent pellet bonding step executed by the pellet bonding mechanism. Thus, the pellet bonding operation as a whole can be done in a reduced period of time.
To attain the second object of the invention, there is provided a pellet bonding apparatus, which comprises a wafer stage capable of installation thereon via a sheet expander of a wafer ring unit having a sheet with wafer division pellets applied thereto, and a pellet removal/transfer mechanism for removing pellets one by one from the wafer ring unit and transferring each removed pellet, the sheet expander including an expander ring formed on an expander base provided on the wafer stage, the expander ring having an end capable of supporting the sheet, the end of the expander ring having a fluid outlet, a press ring disposed outside the expander ring, the press ring being capable of relative axial movement to the expander ring to cause the sheet supported on the end of the expander ring to be expanded to form a gap between adjacent ones of the pellets, and a fluid supply system capable of forming a fluid layer between the sheet and the end of the expander ring by supplying fluid to the fluid outlet.
Thus, according to the invention, with the end of the expander ring formed with a fluid outlet for providing a fluid stream therefrom, a fluid layer can be formed between the sheet and the end of the expander ring. It is thus possible, when the sheet is expanded with the relative movements of the press ring and the expander ring, to extremely reduce the frictional resistance between the sheet and the expander ring with the fluid layer. Consequently, the sheet can be expanded uniformly to form optimum gaps between adjacent ones of pellets.
To attain the first and second objects of the invention, there is provided a pellet bonding apparatus, which comprises a wafer stage capable of installation thereon via a sheet expander of a wafer ring unit having a sheet with wafer division pellets applied thereto, a pellet removal/transfer mechanism for removing pellets one by one from the pellet group of the wafer ring unit at a pellet removal position and transferring each removed pellet, a pellet position correcting mechanism for setting each removed pellet on a rotary table and correcting the position of the pellet, and a bonding mechanism for removing each pellet having been position corrected by the pellet position correcting mechanism and bonding the removed pellet to a lead frame, the wafer stage permitting rotation of the wafer ring unit by each angle corresponding to each of a plurality of areas, which the pellet group of the wafer ring unit is divided into, the pellet position correcting mechanism being capable of correcting pellet position by causing rotation of the rotary table by a predetermined angle in either forward or reverse direction independently of the rotation of the wafer ring unit such that each pellet has the same orientation when removed by the bonding mechanism, the sheet expander including an expander ring formed on an expander base provided on the wafer stage, the expander ring having an end capable of supporting the sheet, the end of the expander ring having a fluid outlet, a press ring disposed outside the expander ring, the press ring being capable of relative axial movement to the expander ring to cause the sheet supported on the end of the expander ring to be expanded to form a gap between adjacent ones of the pellets, and a fluid supply system capable of forming a fluid layer between the sheet and the end of the expander ring by supplying fluid to the fluid outlet.
Thus, according to the invention, when correcting the orientation of a pellet with the rotary table, it is possible to set the angle of rotation of the rotary table that is necessary for the orientation correction to be small, thus curtailing time till the completion of the subsequent pellet bonding step executed by the pellet bonding mechanism. Therefore, the pellet bonding operation as a whole can be done in a reduced period of time. Further, with the formation of the fluid layer between the sheet and the end of the expander ring by fluid flowing out from the fluid outlet formed in the expander ring, it is possible to reduce the frictional resistance between the sheet and the end of the expander ring, thus permitting uniform expanding of the sheet and optimization of the gap between adjacent pellets.